Method For Manufacturing Separator, Separator Manufactured By The Method And Method For Manufacturing Electrochemical Device Including The Separator

ABSTRACT

Disclosed is a method for manufacturing a separator. The method includes (S 1 ) preparing a porous planar substrate having a plurality of pores, (S 2 ) preparing a slurry containing inorganic particles dispersed therein and a polymer solution including a first binder polymer and a second binder polymer in a solvent, and coating the slurry on at least one surface of the porous substrate, (S 3 ) spraying a non-solvent incapable of dissolving the second binder polymer on the slurry, and (S 4 ) simultaneously removing the solvent and the non-solvent by drying. According to the method, a separator with good bindability to electrodes can be manufactured in an easy manner. In addition, problems associated with the separation of inorganic particles in the course of manufacturing an electrochemical device can be avoided.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application No.PCT/KR2011/001371 filed Feb. 25, 2011, which claims priority under 35USC 119(a) to Korean Patent Application Nos. 10-2010-0016990 and10-2011-0016508 filed in the Republic of Korea on Feb. 25, 2010 and Feb.24, 2011, respectively, the entire contents of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a separatorfor an electrochemical device such as a lithium secondary battery, aseparator manufactured by the method, and a method for manufacturing anelectrochemical device including the separator. More specifically, thepresent invention relates to a method for manufacturing a separator inwhich a porous coating layer composed of a mixture of inorganicparticles and binder polymers is formed on a porous substrate, aseparator manufactured by the method, and a method for manufacturing anelectrochemical device including the separator.

BACKGROUND ART

Recently, there has been increasing interest in energy storagetechnologies. As the application fields of energy storage technologieshave been extended to mobile phones, camcorders, notebook computers andeven electric cars, efforts have increasingly been made towards theresearch and development of electrochemical devices. Under thesecircumstances, secondary batteries capable of repeatedly charging anddischarging, in particular, have attracted considerable attention as themost promising electrochemical devices. In recent years, extensiveresearch and development has been conducted to design new electrodes andbatteries for the purpose of improving capacity density and specificenergy of the batteries.

Many secondary batteries are currently available. Lithium secondarybatteries developed in the early 1990's have drawn particular attentiondue to their advantages of higher operating voltages and much higherenergy densities than conventional aqueous electrolyte-based batteriessuch as Ni—MH batteries, Ni—Cd batteries, and H₂SO₄—Pb batteries.However, such lithium ion batteries suffer from safety problems, such asfire or explosion, when encountered with the use of organic electrolytesand have a disadvantage in that they are complicated to manufacture. Inattempts to overcome the disadvantages of lithium ion batteries, lithiumion polymer batteries have been developed as next-generation batteries.More research is still urgently needed to improve the relatively lowcapacities and insufficient low-temperature discharge capacities oflithium ion polymer batteries in comparison with lithium ion batteries.

Many companies have produced a variety of electrochemical devices withdifferent safety characteristics. It is very important to evaluate andensure the safety of such electrochemical devices. The most importantconsideration for safety is that operational failure or malfunction ofelectrochemical devices should not cause injury to users. For thispurpose, regulatory guidelines strictly restrict potential dangers (suchas fire and smoke emission) of electrochemical devices. Overheating ofan electrochemical device may cause thermal runaway or a puncture of aseparator may pose an increased risk of explosion. In particular, porouspolyolefin substrates commonly used as separators for electrochemicaldevices undergo severe thermal shrinkage at a temperature of 100° C. orhigher in view of their material characteristics and productionprocesses including elongation. This thermal shrinkage behavior maycause short circuits between a cathode and an anode.

In order to solve the above safety problems of electrochemical devices,a separator has been suggested in which a mixture of inorganic particlesand a binder polymer is coated on at least one surface of a highlyporous substrate to form a porous organic-inorganic composite coatinglayer. For example, Korean Unexamined Patent Publication No.10-2007-0000231 discloses a technique concerning a separator including aporous substrate and a porous coating layer formed on the poroussubstrate wherein the porous coating layer is composed of a mixture ofinorganic particles and a binder polymer.

The inorganic particles present in the porous coating layer serve asspacers that help to maintain a physical shape of the porous coatinglayer to inhibit the porous substrate from thermal shrinkage when anelectrochemical device overheats or to prevent short circuits betweenboth electrodes of the electrochemical device when thermal runaway takesplace. Interstitial volumes present between the inorganic particles formfine pores.

The presence of a sufficient amount of the inorganic particles above apredetermined level is a prerequisite for the above-mentionedadvantageous functions of the organic-inorganic composite porous coatinglayer formed on the porous substrate. However, an increase in thecontent of the inorganic particles, i.e. a decrease in the content ofthe binder polymer, reduces the bindability of the separator to theelectrodes and tends to cause separation of the inorganic particles fromthe porous coating layer when stress occurs during manufacturing (e.g.,winding) of the electrochemical device or when the separator comes intocontact with an external member. The reduced bindability of theseparator to the electrodes leads to a deterioration in the performanceof the electrochemical device. The separated inorganic particles act aslocal defects of the electrochemical device, giving a negative influenceon the safety of the electrochemical device.

As a result of extensive investigation to solve the problems of theprior art separators, the present applicant has succeeded inmanufacturing a separator which employs a binder polymer having aparticular structure (Korean Patent No. 0754746). There still exists aneed in the art to develop a method for manufacturing a separator withimproved performance.

DISCLOSURE Technical Problem

The present invention is designed to solve the problems of the priorart, and therefore it is an object of the present invention to provide amethod for easily manufacturing a separator with good bindability toelectrodes by which problems associated with the separation of inorganicparticles in the course of manufacturing an electrochemical device canbe avoided. It is another object of the invention to provide a separatormanufactured by the method. It is still another object of the inventionto provide a method for manufacturing an electrochemical deviceincluding the separator.

TECHNICAL SOLUTION

According to an aspect of the present invention, there is provided amethod for manufacturing a separator which includes: (S1) preparing aporous planar substrate having a plurality of pores; (S2) preparing aslurry containing inorganic particles dispersed therein and a polymersolution including a first binder polymer and a second binder polymer ina solvent, and coating the slurry on at least one surface of the poroussubstrate; (S3) spraying a non-solvent incapable of dissolving thesecond binder polymer on the slurry; and (S4) simultaneously removingthe solvent and the non-solvent by drying.

The porous substrate is preferably a porous polyolefin membrane andpreferably has a thickness of 1 to 100 μm.

The inorganic particles preferably have an average particle diameter of0.001 to 10 μm. The inorganic particles may be selected from the groupconsisting of inorganic particles having a dielectric constant of atleast 5, inorganic particles having the ability to transport lithiumions, and mixtures thereof.

The first binder polymer is preferably a polymer having cyano groups. Asthe polymer having cyano groups, there may be mentioned, for example,cyanoethylpullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose,polycyanoacrylate or cyanoethyl sucrose.

Preferably, the solvent used in the preparation of the slurry has asolubility parameter difference of 5.0 Mpa^(0.5) or less from those ofthe first binder polymer and the second binder polymer. Acetone,N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone ormethyl ethyl ketone is more preferably used as the solvent.

As the second binder polymer, there may be mentioned, for example,polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidenefluoride-co-trichloroethylene or polymethyl methacrylate. The differencein solubility parameter between the non-solvent and the second binderpolymer is preferably 8.0 Mpa^(0.5) or more. Particularly, for example,water, methanol or ethanol is more preferably used as the non-solvent.

According to another aspect of the present invention, there is provideda separator manufactured by the method. The separator has a structure inwhich a porous coating layer composed of inorganic particles and amixture of binder polymers is formed on the surface of a poroussubstrate.

According to yet another aspect of the present invention, there isprovided a method for manufacturing an electrochemical device byinterposing the separator between a cathode and an anode, followed bylamination. An electrochemical device manufactured by the method may be,for example, a lithium secondary battery or a supercapacitor device.

ADVANTAGEOUS EFFECTS

The separator manufactured by the method of the present inventionexhibits the following advantageous effects.

First, the non-solvent sprayed on the slurry promotes phase separationof the second binder polymer to allow a larger amount of the secondbinder polymer to be distributed on the surface of the porous coatinglayer. This distribution enhances the bindability of the separator toelectrodes, thus facilitating lamination between the separator and theelectrodes. In addition, problems associated with the separation of theinorganic particles can be avoided.

Second, a sufficiently high bonding strength between the separator andelectrodes is ensured, so that the content of the inorganic particles inthe porous coating layer can be increased, resulting in a furtherimprovement in the stability of the separator.

DESCRIPTION OF DRAWINGS

Other objects and aspects of the present invention will become apparentfrom the following descriptions of the embodiments with reference to theaccompanying drawings in which:

FIG. 1 is a scanning electron microscope (SEM) image showing a porouscoating layer of a separator manufactured in Example 1;

FIG. 2 is a SEM image showing a porous coating layer of a separatormanufactured in Example 2; and

FIG. 3 is a SEM image showing a porous coating layer of a separatormanufactured in Comparative Example 1.

BEST MODE

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

Prior to the description, it should be understood that the terms used inthe specification and the appended claims should not be construed aslimited to general and dictionary meanings, but interpreted based on themeanings and concepts corresponding to technical aspects of the presentinvention on the basis of the principle that the inventor is allowed todefine terms appropriately for the best explanation. Therefore, thedescription proposed herein is just a preferable example for the purposeof illustrations only, not intended to limit the scope of the invention,so it should be understood that other equivalents and modificationscould be made thereto without departing from the spirit and scope of theinvention.

The present invention provides a method for manufacturing a separator.The method of the present invention will now be described in detail.

First, a porous planar substrate having a plurality of pores is prepared(S1).

The porous substrate may be any porous planar substrate commonly used inelectrochemical devices. Examples of such porous planar substratesinclude various porous polymer membranes and non-woven fabrics. As theporous polymer membranes, there can be used, for example, porouspolyolefin membranes used in separators for electrochemical devices,particularly, lithium secondary batteries. The non-woven fabrics may be,for example, those composed of polyethylene phthalate fibers. Thematerial or shape of the porous substrate may vary according to intendedpurposes. Examples of materials suitable for the porous polyolefinmembranes include polyethylene polymers, such as high densitypolyethylene, linear low density polyethylene, low density polyethyleneand ultrahigh molecular weight polyethylene, polypropylene, polybutyleneand polypentene. These polyolefins may be used alone or as a mixturethereof. Examples of materials suitable for the non-woven fabricsinclude polyolefins and polymers having higher heat resistance thanpolyolefins. The thickness of the porous substrate is preferably from 1to 100 μm, more preferably from 5 to 50 μm, but is not particularlylimited to this range. The pore size and porosity of the poroussubstrate are preferably from 0.001 to 50 μm and 10 to 95%,respectively, but are not particularly limited to these ranges.

Subsequently, a slurry containing inorganic particles dispersed thereinand a polymer solution including a first binder polymer and a secondbinder polymer in a solvent is coated on at least one surface of theporous substrate (S2).

Hereinafter, an explanation will be given of the constituent componentsof the slurry used in this step.

The inorganic particles are not specifically limited so long as they areelectrochemically stable. In other words, the inorganic particles can beused without particular limitation in the present invention if they donot undergo oxidation and/or reduction in an operating voltage rangeapplied to an electrochemical device (for example, 0-5 V for Li/Li⁺). Inparticular, a high dielectric constant of the inorganic particles cancontribute to an increase in the degree of dissociation of a salt (e.g.,a lithium salt) in a liquid electrolyte to improve the ionicconductivity of the electrolyte.

For these reasons, it is preferred that the inorganic particles have ahigh dielectric constant of at least 5, preferably at least 10.Non-limiting examples of inorganic particles having a dielectricconstant of at least 5 include BaTiO₃, Pb(Zr,Ti) O₃ (PZT)Pb_(1-x)La_(x)Zr_(1-y)Ti_(y)O₃ (PLZT), Pb(Mg_(1/3)Nb_(2/3)) O₃—PbTiO₃(PMN—PT), hafnia (HfO₂), SrTiO₃, SnO₂, CeO₂, MgO, NiO, CaO, ZnO, ZrO₂,Y₂O₃, Al₂O₃, TiO₂ and SiC particles. These inorganic particles may beused alone or as a mixture of two or more kinds thereof.

The inorganic particles may be those having the ability to transportlithium ions, that is, those containing lithium atoms and having theability to transfer lithium ions without storing the lithium.Non-limiting examples of inorganic particles having the ability totransport lithium ions include lithium phosphate (Li₃PO₄) particles,lithium titanium phosphate (Li_(x)Ti_(y)(PO₄)₃, 0<x<2, 0<y<3) particles,lithium aluminum titanium phosphate (Li_(x)Al_(y)Ti_(z)(PO₄)₃0<x<2,0<y<1, 0<z<3) particles, (LiAlTiP)_(x)O_(y)type glass (0<x<4, 0<y<13)particles such as 14Li₂O—9Al₂O₃—38TiO₂—39P₂O₅ particles, lithiumlanthanum titanate (Li_(x)La_(y)TiO₃, 0<x<2, 0<y<3) particles, lithiumgermanium thiophosphate (Li_(x)Ge_(y)P_(z)S_(w), 0<x<4, 0<y<1, 0<z<1,0<w<5) particles such as Li_(3.25)Ge_(0.25)P_(0.75)S₄ particles, lithiumnitride (Li_(x)N_(y), 0<x<4, 0<y<2) particles such as Li₃N particles,SiS₂ type glass (Li_(x)Si_(y)S_(z), 0<x<3, 0<y<2, 0<z<4) particles suchas Li₃PO₄—Li₂S—SiS₂ particles, and P₂S₅ type glass (Li_(x)P_(y)S_(z),0<x<3, 0<y<3, 0<z<7) particles such as LiI—Li₂S—P₂S₅ particles. Theseinorganic particles may be used alone or as a mixture of two or morekinds thereof.

There is no particular restriction on the average particle diameter ofthe inorganic particles. The average particle diameter of the inorganicparticles is preferably limited to the range of 0.001 to 10 μm. Withinthis range, a uniform thickness and an optimal porosity of the coatinglayer can be obtained. An average particle diameter of less than 0.001μm may cause deterioration of dispersibility. Meanwhile, an averageparticle diameter exceeding 10 μm may increase the thickness of thecoating layer.

The first binder polymer is not specifically limited but is preferably apolymer having cyano groups. Examples of such polymers having cyanogroups include cyanoethylpullulan, cyanoethyl polyvinyl alcohol,cyanoethyl cellulose, polycyanoacrylate and cyanoethyl sucrose. Thesepolymers having cyano groups may be used alone or as a mixture of two ormore thereof. Polyacrylamide-co-acrylate is preferably used as the firstbinder polymer.

The second binder polymer may be selected from the group consisting ofpolyvinylidene fluoride-co-hexafluoropropylene, polyvinylidenefluoride-co-trichloroethylene, polymethyl methacrylate and mixturesthereof.

The weight ratio of the first binder polymer to the second binderpolymer is in the range of 75:25 to 10:90. Within this range, theobjects of the present invention can be suitably achieved. The ratio ofthe weight of the inorganic particles to the weight of the binderpolymers (i.e. the sum of the weights of the first and second binderpolymers) is preferably in the range of 50:50 to 99:1 and morepreferably 70:30 to 95:5. If the inorganic particles are present in anamount of less than 50% by weight (i.e. the binder polymers are presentin a relatively large amount), the pore size and porosity of the porouscoating layer may be reduced. Meanwhile, if the inorganic particles arepresent in an amount exceeding 99% by weight, the peeling resistance ofthe porous coating layer may be deteriorated.

The solvent used in the preparation of the slurry dissolves both thefirst binder polymer and the second binder polymer. The solvent ispreferably one whose solubility parameter has a difference of 5.0Mpa^(0.5) or less from those of the first binder polymer and the secondbinder polymer. Examples of solvents suitable for use in the preparationof the slurry may include acetone, N,N-dimethylacetamide,N,N-dimethylformamide, N-methyl-2-pyrrolidone and methyl ethyl ketone.These solvents may be used alone or as a mixture thereof.

The slurry may be prepared by dissolving the first binder polymer andthe second binder polymer in the solvent, adding the inorganic particlesto the solution, and dispersing the inorganic particles in the solution.The inorganic particles may be crushed to a proper size before additionto the solution of the binder polymers. Preferably, the inorganicparticles are added to the solution of the binder polymers and are thendispersed in the solution while being crushed by a suitable techniquesuch as ball milling.

The slurry thus prepared can be coated on at least one surface of theporous substrate by a technique well-known in the art, for example, dipcoating, roll coating or die coating. Taking into consideration thefunctions of the coating layer and the suitability of the coating layerfor a high-capacity battery, it is preferred to adjust the amount of theslurry loaded on the porous substrate such that the porous coating layerhas a basis weight ranging from 5 to 20 g/m².

Then, a non-solvent incapable of dissolving the second binder polymer issprayed on the slurry coated on the porous substrate (S3). As a resultof the spraying, a non-solvent coating layer is formed on the slurrycoating layer. The term ‘non-solvent’ as used herein refers to a solventthat does not dissolve the second binder polymer. The non-solvent ispreferably one whose solubility parameter has a difference of 8.0Mpa^(0.5) or more from that of the second binder polymer. Particularly,water, methanol or ethanol is more preferred as the non-solvent.

The non-solvent sprayed on the slurry coating layer promotes phaseseparation of the second binder polymer in the slurry to allow a largeramount of the second binder polymer to be distributed on the surface ofthe slurry coating layer. This distribution enhances the bindability ofa separator to be manufactured after subsequent drying (S4) toelectrodes, thus facilitating lamination between the separator and theelectrodes and avoiding problems associated with the separation of theinorganic particles. In addition, a sufficiently high bonding strengthbetween the separator and electrodes is ensured, so that the content ofthe inorganic particles in the porous coating layer can be increased,resulting in a further improvement in the stability of the separator.

Finally, the solvent of the slurry coated on the porous substrate andthe non-solvent are simultaneously removed by drying (S4). Thissimultaneous removal allows a larger amount of the second binder polymerto be present on the outermost surface of the porous coating layer. Thatis, the surface portion of the porous coating layer contains a largernumber of the second binder polymer molecules than the underlyingportion thereof. This distribution enhances the bonding strength betweenthe separator and electrodes.

The slurry coating layer may be dried before spraying with thenon-solvent, unlike in the method of the present invention. In thiscase, however, the function of the non-solvent on the second binderpolymer cannot be expected.

The present invention also provides a separator manufactured by themethod. The separator includes a porous substrate and a porous coatinglayer formed on the porous substrate. The porous substrate and theporous coating layer are the same as those explained earlier. In theporous coating layer, the binder polymers attach (that is, fixedlyconnect) the inorganic particles to each other so as to maintain a statein which the inorganic particles are bound to each other. It ispreferred to maintain a state in which the porous coating layer is boundto the porous substrate by the binder polymers. Thus, the inorganicparticles are in contact with each other in the porous coating layer. Itis preferred that interstitial volumes created between the inorganicparticles in contact with each other become pores of the porous coatinglayer. At this time, the size of the interstitial volumes is equal to orsmaller than the average particle diameter of the inorganic particles.

The present invention also provides a method for manufacturing anelectrochemical device by interposing the separator between a cathodeand an anode, followed by lamination. An electrochemical devicemanufactured by the method may be any device in which electrochemicalreactions occur, and specific examples thereof include all kinds ofprimary batteries, secondary batteries, fuel cells, solar cells, andcapacitors such as supercapacitor devices. Particularly preferred arelithium secondary batteries, including lithium metal secondarybatteries, lithium ion secondary batteries, lithium polymer secondarybatteries and lithium ion polymer secondary batteries.

There is no particular restriction on the production method of a cathodeand an anode to be applied together with the separator of the presentinvention. Each of the electrodes can be produced by binding anelectrode active material to an electrode current collector by suitablemethods known in the art. The cathode active material may be any ofthose that are commonly used in cathodes of conventional electrochemicaldevices. Non-limiting examples of particularly preferred cathode activematerials include lithium manganese oxides, lithium cobalt oxides,lithium nickel oxides, lithium iron oxides and lithium composite oxidesthereof. The anode active material may be any of those that are commonlyused in anodes of conventional electrochemical devices. Non-limitingexamples of particularly preferred anode active materials includelithium, lithium alloys, and lithium intercalation materials such ascarbon, petroleum coke, activated carbon, graphite and othercarbonaceous materials. Non-limiting examples of cathode currentcollectors suitable for use in the electrochemical device of the presentinvention include aluminum foils, nickel foils and combinations thereof.Non-limiting examples of anode current collectors suitable for use inthe electrochemical device of the present invention include copperfoils, gold foils, nickel foils, copper alloy foils and combinationsthereof.

The electrochemical device of the present invention can use anelectrolyte consisting of a salt and an organic solvent capable ofdissolving or dissociating the salt. The salt has a structurerepresented by A⁺B⁻ wherein A+ is an alkali metal cation such as Li⁺,Na⁺, K⁺ or a combination thereof and B is an anion such as PF₆ ⁻, BF₄ ⁻,Cl⁻, Br⁻, ClO₄ ⁻, AsF₆ ⁻, CH₃CO₂ ⁻, N(CF₃SO₂)₂ ⁻, CC(CF₂SO₂)₃ ⁻ or acombination thereof. Examples of organic solvents suitable fordissolving or dissociating the salt include, but are not limited to,propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate(DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane,tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate(EMC) and Υ-butyrolactone. These organic solvents may be used alone oras a mixture thereof.

The electrolyte may be injected in any suitable step duringmanufacturing of the electrochemical device depending on themanufacturing processes and desired physical properties of a finalproduct. Specifically, the electrolyte may be injected before batteryassembly or in the final step of battery assembly.

MODE FOR INVENTION

Hereinafter, the present invention will be explained in detail withreference to embodiments. The embodiments of the present invention,however, may take several other forms, and the scope of the inventionshould not be construed as being limited to the following examples. Theembodiments of the present invention are provided to more fully explainthe present invention to those having ordinary knowledge in the art towhich the present invention pertains.

Example 1

A polymer mixture of cyanoethylpullulan as a first binder polymer andpolyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) as a secondbinder polymer in a weight ratio of 2:10 was dissolved in acetone at 50°C. for at least about 12 hours to prepare a polymer solution. A bariumtitanate (BaTiO₃) powder was added to the polymer solution until theweight ratio of the polymer mixture to the inorganic powder reached10:90. The inorganic particles were crushed and dispersed using a ballmill for at least 12 hours to prepare a slurry. The inorganic particlesof the slurry had an average particle diameter of 600 nm.

The slurry thus prepared was dip-coated on a 12 μm thick porouspolyethylene terephthalate membrane (porosity 45%). The amount of theslurry loaded was adjusted to 12.5 g/m².

Subsequently, distilled water as a non-solvent for the second binderpolymer was sprayed on both surfaces of the slurry. The spray rate ofthe non-solvent was adjusted to 9 mL/min.

Then, the coated substrate was passed through a dryer to remove thesolvent and the non-solvent, completing the manufacture of a separator.The separator was found to have a Gurley value of 373.9 sec/100 mL.

FIG. 1 is a SEM image showing the porous coating layer of the separator.From the image of FIG. 1, it can be confirmed that a large number of thesecond binder polymer molecules were exposed to the surface of theporous coating layer.

Another separator was manufactured as described above. The twoseparators were laminated to each other at 100° C. The laminate wasfound to have a bonding strength of 11.21 gf/cm, implying goodbindability to electrodes.

Example 2

A separator was manufactured in the same manner as in Example 1, exceptthat the kind of the non-solvent was changed to a mixture of distilledwater and methanol (6:4 (v/v)).

FIG. 2 is a SEM image showing the porous coating layer of the separator.From the image of FIG. 2, it can be confirmed that a large number of thesecond binder polymer molecules were exposed to the surface of theporous coating layer.

The separator was found to have a Gurley value of 371.1 sec/100 mL and abonding strength of 9.42 gf/cm.

Example 3

A separator was manufactured in the same manner as in Example 1, exceptthat the kind of the first binder polymer was changed topolycyanoacrylate. The separator was found to have a Gurley value of364.9 sec/100 mL and a bonding strength of 13.10 gf/cm.

Example 4

A separator was manufactured in the same manner as in Example 1, exceptthat the kind of the first binder polymer was changed topolyacrylamide-co-acrylate. The separator was found to have a Gurleyvalue of 361.8 sec/100 mL and a bonding strength of 11.07 gf/cm.

Comparative Example 1

A separator was manufactured in the same manner as in Example 1, exceptthat the non-solvent was not sprayed.

FIG. 3 is a SEM image showing the porous coating layer of the separator.Referring to FIG. 3, a much smaller number of the binder polymermolecules were exposed to the surface of the porous coating layer thanthose observed in the separators of Examples 1 and 2.

Although the Gurley value of the separator was in a good level (382.5sec/100 mL), the bonding strength of the separator was much lower (2.61gf/cm) than the bonding strengths of the separators manufactured inExamples 1-4.

The present invention has been described in detail. However, it shouldbe understood that the detailed description and specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only, since various changes and modifications within thespirit and scope of the invention will become apparent to those skilledin the art from this detailed description.

1. A method for manufacturing a separator, comprising: (S1) preparing aporous planar substrate having a plurality of pores; (S2) preparing aslurry containing inorganic particles dispersed therein and a polymersolution comprising a first binder polymer and a second binder polymerin a solvent, and coating the slurry on at least one surface of theporous substrate; (S3) spraying a non-solvent incapable of dissolvingthe second binder polymer on the slurry; and (S4) simultaneouslyremoving the solvent and the non-solvent by drying.
 2. The methodaccording to claim 1, wherein the porous substrate is a porouspolyolefin membrane.
 3. The method according to claim 1, wherein theporous substrate has a thickness of 1 to 100 μm.
 4. The method accordingto claim 1, wherein the inorganic particles have an average particlediameter of 0.001 to 10 μm.
 5. The method according to claim 1, whereinthe inorganic particles are selected from the group consisting ofinorganic particles having a dielectric constant of at least 5,inorganic particles having the ability to transport lithium ions, andmixtures thereof.
 6. The method according to claim 5, wherein theinorganic particles having a dielectric constant of at least 5 areselected from the group consisting of BaTiO₃, Pb(Zr, Ti)O₃ (PZT),Pb_(1-x)La_(x)Zr_(1-y)Ti_(y)O₃ (PLZT, 0<x<1, 0<y<1),Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃ (PMN—PT), hafnia (HfO₂), SrTiO₃, SnO₂,CeO₂, MgO, NiO, CaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, SiC, TiO₂ particles, andmixtures thereof.
 7. The method according to claim 5, wherein theinorganic particles having the ability to transport lithium ions areselected from the group consisting of lithium phosphate (Li₃PO₄),lithium titanium phosphate (Li_(x)Ti_(y)(PO₄)₃, 0<x<2, 0<y<3), lithiumaluminum titanium phosphate (Li_(x)Al_(y)Ti_(x)(PO₄)₃, 0<x<2, 0<y<1,0<z<3), (LiAlTiP)_(x)O_(y) type glass (0<x<4, 0<y<13), lithium lanthanumtitanate (Li_(x)La_(y)TiO₃, 0<x<2, 0<y<3), lithium germaniumthiophosphate (Li_(x)Ge_(y)P_(z)S_(w), 0<x<4, 0<y<1, 0<z<1, 0<w<5),lithium nitride (Li_(x)N_(y), 0<x<4, 0<y<2), SiS₂ type glass(Li_(x)Si_(y)S_(z), 0<x<3, 0<y<2, 0<z<4), P₂S₅ type glass(Li_(x)P_(y)S_(z), 0<x<3, 0<y<3, 0<z<7) particles, and mixtures thereof.8. The method according to claim 1, wherein the first binder polymer isa polymer having cyano groups.
 9. The method according to claim 8,wherein the polymer having cyano groups is selected from the groupconsisting of cyanoethylpullulan, cyanoethyl polyvinyl alcohol,cyanoethyl cellulose, polycyanoacrylate, cyanoethyl sucrose and mixturesthereof.
 10. The method according to claim 1, wherein the first binderpolymer is polyacrylamide-co-acrylate.
 11. The method according to claim1, wherein the solvent has a solubility parameter difference of 5.0Mpa^(0.5) or less from those of the first binder polymer and the secondbinder polymer. 15
 12. The method according to claim 11, wherein thesolvent is selected from the group consisting of acetone,N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone,methyl ethyl ketone and mixtures thereof.
 13. The method according toclaim 1, wherein the second binder polymer is selected from the groupconsisting of polyvinylidene fluoride-co-hexafluoropropylene,polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylateand mixtures thereof.
 14. The method according to claim 1, wherein thedifference in solubility parameter between the non-solvent and thesecond binder polymer is 8.0 Mpa^(0.5) or more.
 15. The method accordingto claim 14, wherein the non-solvent is selected from the groupconsisting of water, methanol, ethanol and mixtures thereof.
 16. Themethod according to claim 1, wherein the first binder polymer and thesecond binder polymer is in a weight ratio of 75:25 to 10:90.
 17. Themethod according to claim 1, wherein the inorganic particles and thebinder polymers is in a weight ratio of 50:50 to 99:1.
 18. A separatormanufactured by the method according to claim
 1. 19. A method formanufacturing an electrochemical device, the method comprisinginterposing a separator manufactured by the method according to claim 1between a cathode and an anode, followed by lamination.
 20. The methodaccording to claim 19, wherein the electrochemical device is a lithiumsecondary battery.